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United States Patent |
5,050,012
|
Nishiumi, ;, , , -->
Nishiumi
,   et al.
|
September 17, 1991
|
High-speed erasing apparatus for use in magnetic recording/reproducing
system
Abstract
A high-speed erasing apparatus for use in a magnetic recording/reproducing
system for erasing a recorded signal on a magnetic tape traveling along a
predetermined path. The erasing apparatus comprises a flying-erasing head
mounted on a rotary cylinder of the system, a full-erasing head disposed
at a preceding position of the flying-erasing head in a traveling
direction of the tape, and an audio-erasing head provided at a succeeding
position thereof in the traveling direction. Also included in the
apparatus are a high-speed erase oscillating circuit for supplying the
full-erasing head with an output having a frequency higher than N times of
the upper limit of the audible range, a video-erase oscillating circuit
for supplying the flying-erasing head with an output having a frequency
higher than the upper limit of a video signal range, and an audio-erase
oscillating circuit for supplying the audio-erasing head with an output
having a frequency higher than the upper limit of the audible range. The
oscillating circuits are driven so that, at the initial time, the recorded
signal is erased by all of the erasing heads with the tape being
transported at the industry standard traveling speed and the high-speed
erase oscillating circuit is operated so as to, after elapse of a
predetermined time, erase the recorded signal by only the full-erasing
head with the tape being transported at N times of the industry standard
traveling speed.
Inventors:
|
Nishiumi; Hiroshi (Kawasaki, JP);
Namiki; Yasuomi (Yokohama, JP)
|
Assignee:
|
Victor Company of Japan, Ltd. (JP)
|
Appl. No.:
|
340308 |
Filed:
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April 19, 1989 |
Foreign Application Priority Data
Current U.S. Class: |
360/66 |
Intern'l Class: |
G11B 005/03 |
Field of Search: |
360/66
|
References Cited
U.S. Patent Documents
4527202 | Jul., 1985 | Ohta | 360/66.
|
4737865 | Apr., 1988 | Murakami et al. | 360/66.
|
4750060 | Jun., 1988 | Nakazawa et al. | 360/66.
|
Primary Examiner: Canney; Vincent P.
Attorney, Agent or Firm: Lowe, Price, LeBlanc & Becker
Claims
What is claimed is:
1. A high-speed erasing apparatus for use in a magnetic
recording/reproducing system for erasing recorded signals including a
video signal and an audio signal in an audible frequency range on a
magentic tape with said magnetic tape being transported by drive means at
N times as high as an industry standard travelling speed of said magentic
tape where N is a positive number, said magnetic recording/reproducing
system including a rotational cylinder around which said magentic tape is
wrapped, said high-speed erasing apparatus comprising:
erasing head means comprising a flying-erasing head mounted on said
rotational cylinder, a full-erasing head provided at a preceding position
of said flying-erasing head with respect to a travelling direction of said
magnetic tape, and an audio-erasing head provided at a succeeding position
of said flying-erasing head with respect to said travelling direction of
said magentic tape, said magentic tape travelling in contact relation to
said erasing head means;
a high-speed erase oscillating circuit for supplying said full-erasing head
with an oscillation output having a frequency higher than N times an upper
limit of the audible frequency range;
a video-erase oscillating circuit for supplying said flying-erasing heat
with an oscillation output having a frequency higher than an upper limit
of a carrier frequency range of the video signal;
an audio-erase oscillating circuit for supplying said audio-erasing head
with an oscillation output having a frequency higher than the upper limit
of the audible range; and
a control circuit coupled to said drive means and said oscillating
circuits, for causing said oscillating circuits and said drive means being
controlled so that, at an initial state, the recorded signals are erased
by said erasing head means with said magnetic tape being transported at
the industry standard travelling speed and for subsequently causing after
elapse of a predetermined time, said high-speed erase oscillating circuit
and said drive means being controlled that the recorded signals are erased
by only said full-erasing head with said magentic tape being transported
at a speed changed to N times the industry standard travelling speed.
2. A high-speed erasing apparatus as claimed in claim 1, wherein said
high-speed erase oscillating circuit comprises a first oscillator which
generates a first output having a first frequency, a second oscillator
which generates a second output having a second frequency different from
said first frequency and a switching circuit coupled to said first and
second oscillators for performing a switching operation between said first
and second outputs of said first and second oscillators, either said first
or second output thereof being supplied as the oscillation output of said
high-speed oscillating circuit to said full-erasing head in accordance
with the switching operation of said switching circuit which is under
control of said control circuit.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to a high-speed erasing apparatus
for use in helical scanning type magnetic recoding/reproducing systems
such as a video tape recorder (VTR).
A helical-scanning type VTR is generally arranged to include a rotational
cylinder, having at its circumferential portions a plurality of magnetic
heads, around which a magentic tape is wound or wrapped obliquely so as to
perform recording or reproducing bf information on and from the magnetic
tape by the magnetic heads in accordance with traveling of the magnetic
tape concurrently with rotation of the rotational cylinder. Furthermore,
known is a depth-recording type Hi-Fi VTR having on its rotational
cylinder an audio head and a video head which are disposed to be close to
each other. The depth-recording type Hi-Fi VTR is arranged such that an
audio signal is recorded at a depth of a magnetic layer of the tape by the
audio head and a video signal is further recorded (overwritten) over the
recorded audio signal by the video head, whereby as shown in FIG. 5 the
video signal and the audio signal are recorded successively along an
oblique track T formed by the audio and video heads on the helically
guided magnetic tape T.sub.P with a video signal segment of every field.
In addition to the audio head 3 and the video head 2, the aforementioned
VTR is provided with an audio signal recording fixed head which in turn
records an audio signal on a side edge portion of the magnetic tape
T.sub.P with it slidably contacting the traveling magentic tape T.sub.P so
as to form an audio track T.sub.A. Also included generally in the
aforementioned VTR is a full-erasing head 1 for a full-tape width erasure
of the magnetic tape T.sub.P which is adapted to erase the previously
magnetic signals, before performing recording of a new signal on the
magnetic tape T.sub.P.
However, there is a problem which arises with such a VRT in that, because
the full-width-erasing head 1 is disposed stationarily to take a preceding
position to the video head 2 and the audio head 3 mounted on the
rotational cylinder with respect to the tape travel direction, in the
cases where the erasing operation is started upon determination of the
erasing position determined from a reproduced picture image, a non-erased
portion (shadowed portion in FIG. 5) is developed unintentionally between
the position of a track recorded with the signal of the reproduced picture
image and the full-erasing head 1, thereby resulting in the problem of
incomplete erasure of the signal.
One conceivable solution for elimination of the presence of the non-erased
portion left on the magentic tape T.sub.P is to set a recording condition
without supplying the video signal and audio signal but with erasing
signals to the video head 2 and the audio head 3 and let both heads carry
on an erasing operation without using full erasing head. In this instance,
it takes a longer time, i.e., the same time as normal signal recording
operation, thus it would be unable to perform a high-speed erasing
operation.
In addition, such a VTR is generally so arranged that the frequency of the
erasing current to be supplied to the full-erasing head 1 is about five
times (about 70 KHz) the upper limit of the audible frequency range. In
this case another problem arises in that upon reproduction of the tape,
the frequency of the erasing current is derived in the audible range as
disturbing noises.
SUMMARY OF THE INVENTION
The present invention has been developed in order to remove the drawbacks
inherent to the conventional high-speed erasing apparatus for magnetic
recording/reproducing system.
It is therefore an object of the present invention is to provide a
high-speed erasing apparatus for use in a magentic recording/reproducing
system which does not produce the non-erased portion and which is capable
of eliminating the frequency component of the erasing current on
reproduction.
With this and other objects which will become apparent as the description
proceeds, a high-speed erasing apparatus for use in a magnetic
recording/reproducing system according to the present invention includes a
flying-erasing head mounted on a rotational cylinder of the magnetic
recording/reproducing system, a full-erasing head disposed at a preceding
position of the flying-erasing head with respect to a traveling direction
of a magnetic tape, and an audio-erasing head provided at a succeeding
position of the flying-erasing head with respect to the traveling
direction of the magnetic tape which is transported to be wrapped around
the rotational cylinder in contact relation to the respective erasing
heads. The apparatus further includes a high-speed erase oscillating
circuit for supplying the full-erasing head with an oscillator output
having a frequency higher than N times is the upper limit of the audible
range where N is a positive number, a video-erase oscillating circuit for
supplying the flying-erasing head with an oscillator output having a
frequency higher than the upper limit of a carrier frequency range of a
video signal, and an audio-erase oscillating circuit for supplying the
audio-erasing head with an oscillator output having a frequency higher
than the upper limit of the audible range. Also included in the apparatus
is a control circuit coupled to the oscillating circuits, the control
circuit for causing the oscillating circuits to be controlled so that, at
the initial state of the erasing operation, the recorded signals are
erased by means of all the erasing heads with the magnetic tape being
transported at the industry standard traveling speed and then causing the
high-speed erase oscillating circuit to be driven so that, after elapse of
a predetermined time, the recorded signals are erased by only the
full-erasing head with the magnetic tape being driven at a speed changed
to N times the industry standard traveling speed.
Preferably, the high-speed erase oscillating circuit comprises a first
oscillator which generates a first output having a first frequency, a
second oscillator which generates a second output having a second
frequency different from the first frequency and a switching circuit
coupled to the first and second oscillators for performing a switching
operation between the first and second outputs of the first and second
oscillators, either the first or second output thereof being supplied as
the oscillation output of the high-speed oscillating circuit to the
full-erasing head in accordance with the switching operation of the
switching circuit which is under control of the control circuit.
BRIEF DESCRIPTION OF THE DRAWINGS
The object and features of the present invention will become more readily
apparent from the following detailed description of the preferred
embodiments taken in conjunction with the accompanying drawings in which:
FIG. 1 is a block diagram showing an high-speed erasing apparatus according
to an embodiment of the present invention;
FIG. 2 is an illustration for describing the relation in position on a
magnetic tape between the respective erasing heads of the FIG. 1
high-speed erasing apparatus;
FIG. 3 is a circuit diagram illustrating a circuit arrangement of the FIG.
1 high-speed erasing apparatus;
FIG. 4 is a time chart for describing operation of the FIG. 1 high-speed
erasing apparatus; and
FIG. 5 shows a general track pattern and the positions of heads therefor.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to FIG. 1, there is schematically illustrated the arrangement
of a high-speed erasing apparatus for magnetic recording/reproducing
system according to an embodiment of the present invention. In FIG. 1, the
high-speed erasing apparatus is adapted to perform a high-speed erasing
operation with a magnetic tape T.sub.P traveling at a high speed ten times
as high as a regular tape traveling speed (one of the industry standard
speeds for example, 3.34 cm/sec) on reproduction or on recording. The
arrangement comprises a full-erasing head 5, a flying-erasing head 6 and
an audio-erasing head 7. The flying-erasing head 6 is mounted on a
rotational cylinder C so as to contact with the magnetic tape T.sub.P
wrapped around the rotational cylinder C, and the full-erasing head 5 and
audio-erasing head 7 are respectively positioned stationary at the outside
of the rotational cylinder C. These erasing heads 5, 6 and 7, as will be
apparent from FIG. 1 or 2, are disposed in sequence to come into contact
with the magnetic tape T.sub.P traveling in a predetermined direction. The
high-speed erasing apparatus is further provided with a high-speed erase
oscillating circuit 8, an audio erase oscillating circuit 9 and a video
erase oscillating circuit 10 which are in turn. under control of a control
circuit 11. The audio erase oscillator circuit 9 supplies the
audio-erasing head 7 with an oscillation output (erasing current) having a
frequency of about 70 KHz which is about five times the upper limit of the
audible range, and the video erase oscillating circuit 10 supplies the
flying-erasing head 6 with an oscillation output having a frequency of
about 11 MHz which is above the frequency range of the video signal to be
recorded or reproduced. On the other hand, the high-speed erase
oscillating circuit 8 comprises a first oscillator 12 for generating an
output having a frequency of about 70 KHz, a second oscillator 13 for
generating an output having a frequency of about 170 KHz which is higher
than ten times the upper limit of the audible range, and a switching
circuit 14 for selectively performing a switching operation between the
first and second oscillators 12 and 13 so as to supply either the
oscillation output of the first oscillator 12 or the oscillation output of
the second oscillator 13 to the full-erasing head 5. The first and second
oscillators 12, 13 and the switching circuit 14 are driven under control
of the control circuit 11.
FIG. 3 shows detailed arrangements of the high-speed erase oscillating
circuit 8 and the control circuit 11. The first oscillator 12 of the
high-speed erase oscillating circuit 8 comprises a blocking oscillating
circuit equipped with a transformer Tl for oscillation, transistor Trl and
a capacitor Cl. The primary coil of the transformer Tl receives a power
supply current through a midpoint tap and one end thereof is coupled to
the base of the transistor Trl through a time-constant circuit comprising
a capacitor C2 and a resistor Rl and further grounded through a capacitor
C3. The other end of the primary coil thereof is connected to the
collector of the transistor Trl. One end of the secondary coil of the
transformer Tl is grounded and the other end thereof is coupled to the
switching circuit 14 so as to form a signal line through which the output
of the first oscillator 12 is supplied to the switching circuit 14.
The capacitor Cl is disposed between both the ends of the secondary coil of
the transformer Tl, and the capacity of the capacitor Cl and the
inductance of the transformer Tl are determined so that the oscillation
frequency of the or 12 is about 70 KHz being five times the first
oscillator 12 is about 70 KHz being five times the upper limit (generally,
about 15 KHz) of the audible range. Furthermore, the second oscillator 13,
as well as the first oscillator 12, is provided with a transformer T2 for
oscillation, two transistors Tr2, Tr3 making up an astable multivibrator,
and with a capacitor C4. The primary coil of the transformer T2 receives a
power supply current through a midpoint tap and one end thereof is
connected to the collector of the transistor Tr2 and further connected to
base of the transistor Tr3 through a time-constant circuit comprising a
capacitor C5 and a resistor R3. On the other hand, the other end of the
primary coil is coupled to the collector of the transistor Tr3 and further
coupled to the base of the transistor Tr2 through a time-constant circuit
comprising a capacitor C6 and a resistor R4. Here, the emitters of the
transistors Tr2 and Tr3 are grounded through a resistor R5 and the bases
of the transistors Tr2 and Tr3 are coupled to each other through a
capacitor C7.
One end of the secondary coil of the transformer T2 is grounded and the
other end thereof is coupled to the switching circuit 14 so as to form a
signal line through which the oscillation output of the second oscillator
13 is supplied to the switching circuit 14. In addition, the capacitor C4
is disposed between both the ends of the secondary coil thereof, and in
this embodiment the capacity of the capacitor C4 and the inductance of the
transformer T2 are appropriately determined so that the oscillation
frequency of the second oscillator 13 becomes about 170 KHz which is over
ten times the upper limit of the audible range.
Here, in the case where that the ten-times speed erasure is performed with
the oscillation output of the second oscillator 13, when the erased
portion is reproduced at a regular tape traveling speed (one of the
industry standard speeds) the frequency of the reproduction output falls
within the carrier frequency range of a recorded FM-modulated luminance
signal, the reproduction output component of the erasing current appears
as noise on the reproduced picture image. Therefore, it is preferable that
the oscillation output of the second oscillator 13 is determined so that
the frequency of the reproduction output is out of the carrier frequency
range. That is, in cases where the ten-time speed erasure is effected
under the conditions that the carrier range of the FM modulated luminance
signal is 3.4 to 4.4 MHz, the relative speed of the video head with
respect to the magnetic tape T.sub.P is 5.8 m/sec and the regular tape
traveling speed is 3.34 cm/sec, the recorded wavelength of the
FM-modulated luminance signal to be recorded on the magnetic tape T.sub.P
becomes 1.71 [micrometer](5.8 divided by 3.4.times.106 to 1.32
[micrometers](5.8 divided by 4.4.times.106), and therefore, the frequency
of the erasing current on the high-speed erase is set to be below 195
[KHz](3.34.times.10.sup.-2 .times.10 divided by 1.71.times.10.sup.-6) or
be above 253 [KHz](3.34.times.10.sup.-2 .times.10 divided by
1.32.times.10.sup.-6).
Furthermore, the the oscillation frequency of the second oscillator 13 is
required to be set to be above 150 [KHz](15.times.10) so that the
frequency of the reproduction output on reproduction of the ten-times
high-speed erased portion becomes out of the audible range (about 20 Hz to
15 KHz). Thus, the oscillation frequency of the second oscillator 13 in
performing the ten-times high-speed erasure may be set to a value which
satisfy the above-mentioned conditions, i.e., a value (for example, 170
KHz) which is above 150 KHz and below 195 KHz.
On the other hand, the control circuit 11 includes first to fifth
transistors Tr4, Tr5, Tr6, Tr7 and Tr8 and a control signal generating
circuit 15. The first transistor Tr4 is coupled in series to the other
transistors Tr5 to Tr8, as shown in FIG. 3, so as to turn on and off power
supply lines between a power supply terminal 16 coupled to a power supply
of 12 V and the respective oscillating circuits 9, 10, 12 and 13. From the
control signal generating circuit 15 to the respective bases of the first
to fifth transistors Tr4 to Tr8 are supplied first to fifth control signal
Sl to S5 as illustrated by (A) to (E) in FIG. 4. The respective
transistors Tr4 to Tr8 are on-off-controlled in response to these control
signals Sl to S5, whereby the respective oscillators 9, 10, 12 and 13 are
driven accordingly. Here, control signal generating circuit 15 produces
the first to fifth control signals Sl to S5 in accordance with a mode
signal supplied thereto through an input terminal 17.
Furthermore, in this embodiment the output of the second transistor Tr5 is
a switching control signal S6 illustrated by (F) in FIG. 4, which is in
turn supplied to the switching circuit 14. When the switching control
signal S6 is in the low-level state, the oscillation output of the first
oscillator 12 is supplied to the full-erasing head 5, and whencoming to
the high-level state, the oscillation output of the second oscillator 13
is supplied thereto.
A description will be given hereinbelow in terms of high-speed erase
operation of the above-mentioned high-speed erasing apparatus. In response
to a start of the high-speed erasing operation, the magentic tape T.sub.P
is driven initially at a regular traveling speed by means of a drive
mechanism, not shown, and the control signals Sl, S3, S4 and S5 shown by
(A), (C), (D) and (E), which are generated by the control signal
generating circuit in response to a high-speed erase mode signal inputted
to the input terminal 17, respectively enter in the low-level states
whereby the first, third, fourth and fifth transistors Tr4, Tr6, Tr7 and
Tr8 are set to ON-states, respectively. Thus, a power supply current from
the power supply terminal 16 is applied to the first oscillator 12 of the
high-speed erase oscillating circuit 8, audio erase oscillating circuit 9
and video erase oscillating circuit 10, respectively. In response to the
power supply current, the oscillating circuits 12, 9 and 10 are driven so
as to generate the oscillation outputs which are in turn supplied to the
full-erasing head 5, audio-erasing head 7 and flying-erasing head 6,
respectively. Here, at this time, the second transistor Tr5 is in the
OFF-state, and the switching control signal S6 is in the low-level state
as shown by (F) in FIG. 4.
After elapse of a predetermined time t, when the erased portion due to the
.full-erasing head-5 reaches, the position of the audio-erasing head 7,
the traveling speed of the magentic tape T.sub.P is automatically switched
to ten times the regular traveling speed by the drive mechanism in
response to a tape speed control signal generated in correspondence with
the predetermined time t by the control signal generating circuit 15 and
supplied to the drive mechanism through a terminal 18 in FIG. 3. At the
same time, as shown in FIG. 4, the control signal S2 changes from the
high-level state to the low-level state, the switching control signal S6
varies from the low-level state to the high-level state, and further the
control signals S3 to S5 change from the low-level states to the
high-level states, respectively. Therefore, the third to fifth transistors
Tr6 to Tr8 are turned off and the second transistor Tr5 is turned on,
whereby the power supply current from the power supply terminal 16 is
supplied to the second oscillator 13 of the high-speed erase oscillating
circuit 8 and to the switching circuit 14 to make the latter to be
activated so that the oscillation output of the second oscillator 13 is
supplied to the full-erasing head 5.
Thereafter, such high-speed erasing operation continues and, in response to
termination of the erase, the control signals Sl to S5 change to the
high-level states and the switching control signal S6 enters in the
low-level state. Here, the predetermined time t is about 7 seconds under
the conditions that the regular tape traveling speed is 3.34 cm/sec and
the distance on the magnetic tape T.sub.P from the full-erasing head 5 to
the audio-erasing head 7 is 230.3 mm. Furthermore, in the case of
reproduction with so-called three-times recording and play time mode,
since the tape traveling speed becomes 7/8 of the regular traveling speed,
the predetermined time t becomes about 21 seconds (7 sec.times.3).
On the other hand, in the case of performing the regular recording by the
above-mentioned high-speed erasing apparatus, as shown in FIG. 4, the
first and third to fifth control signals Sl, S3 to S5 are respectively set
to be in the low-level states, and the oscillation outputs of about 70 KHz
from the first oscillator 12 of the high-speed erase oscillating circuit 8
and from the audio erase oscillating circuit 9 are supplied to the
full-erasing head 5 and the audio-erasing head 7 respectively, and the
oscillation output of about 11 MHz from the video erase oscillating
circuit 10 is supplied to the flying-erasing head 6. In addition, for
insert edit (a part of track or tracks is overrecorded with a new signal
replacing the previously recorded portion by simultaneously erasing
thereof) of a video signal, only the first and fourth control signals Sl
and S4 enter in the low-level states and only the flying-erasing head 6
performs the erasing operation. On the other hand, for after recording
operation with an audio signal, only the first and fifth control signals
Sl and S5 become to the low-level states and only the audio-erasing head 7
becomes the erasing state.
As described above, in the high-speed erasing apparatus according to this
embodiment, high-speed erasure can be performed without developing or
leaving non-erased portions by cleverly controlling the tape transport
speed, the full-erasing head 5, flying erasing head 6 and audio-erasing
head 7. In addition, since the frequency of the erasing current for the
high-speed erasing operation is set to be 170 KHz, in the case that the
high-speed-erased portion is reproduced at the regular speed, the
reproduction output component of the erasing current becomes above the
upper limit of the audible range and below the carrier range of a
FM-modulated luminance signal, and therefore the reproduction output
component does not cause noise and does not appear as noise on the
reproducted picture image. Furthermore, although the power consumption of
the second oscillator 13 in which oscillation is effected with a relative
high frequency is greater as compared with that of the first oscillator
12, since the second oscillator 13 is driven only in the high-speed
erasing mode, it is possible to significantly save power as compared with
the condition that the second oscillator 13 is always kept operated.
Furthermore, although in this embodiment oscillation of about 170 KHz is
made by using a power supply of 12 V and hence the voltage at both ends of
the secondary coil of the transformer T2 of the second oscillator 13
reaches 120 Vp-p, since the transistors Tr2 and Tr3 of the primary coil
thereof is used so as to form a two-step arrangement, it is possible to
prevent these transistors Tr2 and Tr3 from being damaged, thereby
resulting in improving the reliability of the high-speed erasing
apparatus.
Furthermore, although in this embodiment the audio erase oscillating
circuit 9 and the first oscillator 12 are provided separately, it is also
possible that a single oscillating circuit which generates an oscillation
output of about 70 KHz is used for both the audio-erasing head 7 and
full-erasing head 5. In addition, although in this embodiment the
frequency of the erasing current for erasing operation is switched between
70 KHz and 170 KHz, however, for the high-speed erase operation, only the
erasing current only for the regular speed erasure.
It should be understood that the foregoing relates to only a preferred
embodiment of the present invention, and that it is intended to cover all
changes and modifications of the embodiment of this invention herein used
for the purposes of the disclosure, which do not constitute departures
from the spirit and scope of the invention.
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